There are many applications where so-called composite structures find utility. For instance, filament-reinforced composite materials are utilized to provide strong lightweight aircraft components. One of the most demanding applications for a composite aircraft component is in providing a link for connecting a rotor to a hub in a helicopter rotor system.
In connecting a rotor to a hub, the link must be capable of sustaining not only the substantial axial loads imparted by the centrifugal force acting on the rotor but also two plane bending and shear loads. In addition, the link must also have sufficiently low torsional stiffness as to permit the attack angle of the rotor to be adjusted as it rotates. A satisfactory composite link should also be light in weight, have a long service life, be relatively failsafe, and be capable of being manufactured economically.
It is known that in designing a composite tubular member for use as a torsion link, it is desirable for the filaments to be wound at a low angle, i.e. for the filaments to extend substantially axially, relative to the longitudinal axis of the link to provide a tubular structure which is strong in tension and flexurally stiff. Such a disposition of filaments, however, causes the tubular structure to have a relatively low shear stiffness. While shear stiffness can be increased by increasing the winding angle, increasing the winding angle also increases the torsional stiffness of the structure and reduces its flexural stiffness. Because of this, it has been difficult to design a filament-wound tubular composite torsion link which is axially strong, stiff in flexure and transverse shear, and low in torsional stiffness.